THE REGULATORY FUNCTIONS OF THE GAMMA-SUBUNIT AND EPSILON-SUBUNIT FROM CHLOROPLAST CF1 ARE TRANSFERRED TO THE CORE COMPLEX, ALPHA(3)BETA(3), FROM THERMOPHILIC BACTERIAL F1

The expression plasmids for the subunit gamma (gamma(c)) and the subun it epsilon (epsilon(c)) of chloroplast coupling factor (CF1) from spin ach were constructed, and the desired proteins were expressed in Esche richia coli, Both expressed subunits were obtained as inclusion bodies , When recombinant gamma(c) was mixed with recombinant alpha and beta subunits of F-1 from thermophilic Bacillus PS3 (TF1), a chimeric subun it complex (alpha(3) beta(3) gamma(c)) was reconstituted and it showed significant ATP hydrolysis activity. The ATP hydrolysis activity of t his complex was enhanced in the presence of dithiothreitol and suppres sed by the addition of CuCl2, which gamma(c). Hence, this complex has induces formation of a disulfide bond between two cysteine residues in similar modulation characteristics as CF1. The effects of recombinant epsilon(c) and epsilon subunit from TF1 (epsilon(t)) on alpha(3) beta (3) gamma(c) were also investigated. epsilon(c) strongly inhibited the ATP hydrolysis activity of chimeric alpha(3) beta(3) gamma(c) complex but epsilon(t) did not. The inhibition was abolished and the ATP hydr olysis activity was recovered when methanol was added to the assay med ium, The addition of epsilon(c) or epsilon(t) to the alpha(3) beta(3) gamma(t) complex, which is the authentic subunit complex from TF1, res ulted in weak stimulation of the ATP hydrolysis activity. These result s suggest that (a) the specific regulatory function of gamma(c) can be transferred to the bacterial subunit complex: (b) the interaction bet ween the gamma(c) subunit and epsilon(c) strongly affects the enzyme a ctivity, which was catalyzed at the catalytic sites that reside on the alpha(3) beta(3) core.